Problem painting component

[Leonardo Fernandes]

Hello, I made a component called GradientLegend but I am having trouble to properly display it on a JFrame. The component is painted and immediately after disappears, leaving the frame empty (at least that's what happens when I compile and run the code below with java 1.4.1 for linux). By the tutorials I've been through the code seems to be right, does anyone find what's wrong? The code follows.
Thanks.

import java.awt.*;
import javax.swing.*;
import java.text.NumberFormat;
class GradientLegend extends JPanel{
    private final int COLORSTEP = 5;
    private final int PIXELSTEP = 5;
    private final int WIDTH = 10;
    private final int MAXCOLOR = 255;
    private final int MINCOLOR = 0;
    private boolean isVertical;
    private String unit;
    private double min;
    private double max;
    private int x;
    private int y;
    public GradientLegend(int inx, int iny, boolean vertical,double min, double max, String u){
Dimension d = new Dimension();
isVertical = vertical;
x = inx;
y = iny;
unit = u;
if(vertical){
    d.setSize(40,200);
    this.setPreferredSize(d);
}
else{
    d.setSize(200,40);
    this.setPreferredSize(d);
}
    }
    public void paintComponent(Graphics g){
int red=MINCOLOR;
int green=MINCOLOR;
int blue=MAXCOLOR;
super.paintComponent(g);
Font f = new Font("SansSerif",Font.PLAIN, 10);
g.setFont(f);
g.drawString(min + unit,x+20,y);
NumberFormat nf = NumberFormat.getNumberInstance();
nf.setMaximumFractionDigits(2);
nf.setMinimumFractionDigits(2);
if(isVertical){
    g.setColor(Color.black);
    g.drawString(nf.format(min) + unit,x+15,y);
    while(green <= MAXCOLOR){
g.setColor(new Color(red,green,blue));
g.fillRect(x,y,WIDTH,PIXELSTEP);
green += COLORSTEP;
y += PIXELSTEP;
    }
    green = MAXCOLOR;
    g.setColor(Color.black);
    g.drawString(nf.format(min + ((max - min)/4)) + unit,x+15,y);
    blue -= COLORSTEP;
    while(blue >= MINCOLOR){
g.setColor(new Color(red,green,blue));
g.fillRect(x,y,WIDTH,PIXELSTEP);
blue -= COLORSTEP;
y += PIXELSTEP;
    }
    blue = MINCOLOR; red += COLORSTEP;
    g.setColor(Color.black);
    g.drawString(nf.format(min + ((max - min)/2)) + unit,x+15,y);
    while(red <= MAXCOLOR){
g.setColor(new Color(red,green,blue));
g.fillRect(x,y,WIDTH,PIXELSTEP);
red += COLORSTEP;
y += PIXELSTEP;
    }
    red = MAXCOLOR;
    g.setColor(Color.black);
    g.drawString(nf.format(min + ((max - min)*(3/4))) + unit,x+15,y);
    green -= COLORSTEP;
    while(green >= MINCOLOR){
g.setColor(new Color(red,green,blue));
g.fillRect(x,y,WIDTH,PIXELSTEP);
green -= COLORSTEP;
y += PIXELSTEP;
    }
    g.setColor(Color.black);
    g.drawString(nf.format(max) + unit,x+15,y);
}
    }
}

public class Teste{
    public static void main(String[] args){
GradientLegend legend;
JFrame frame;
Container cont;
Toolkit tk = Toolkit.getDefaultToolkit();
Dimension d = tk.getScreenSize();
frame = new JFrame("Gradient Test");   
frame.setSize((d.width*2)/3,(d.height*2)/3);
cont = frame.getContentPane();
cont.setLayout(new BorderLayout());
legend = new GradientLegend(2, 2, true, 1, 100, "kbps");
cont.add("Center",legend);
frame.show(); // after this call, component is painted 
                      // and mmedietly disappears...
    }
}

[Ernest Friedman-Hill]

Hi,
Welcome to JavaRanch!
I'm not sure why you're passing in the x,y location of the component as constructor parameters; in any case, the problem is that these are wrong as soon as the container is laid out. The wrong coordinates lead to the image being drawn in an offscreen location, so you can't see it.
Instead of passing in x, y, use getLocation().x and getLocation().y in paintComponent(). You should find that your program works perfectly.

[Leonardo Fernandes]

Thanks for your help, I just found out what the problem was. I use x and y as parameters for the caller to decide where does it want to show the gradient. In the paintComponent() method I was increasing y all the time, and when the component was repainted (which seems to happen right after the first paint), y was greater then the component height. I set y to it original value at the end of paintComponent() and now it works fine. By the way, how do I become something better than a greenhorn?

[Ernest Friedman-Hill]

You automatically get to be a "ranch hand" after you've posted some number of times -- 30 times, I think? If you want something more colorful than that, you can either work very hard and be elected a bartender... or you can take the easy way out!